Foaming rate

Halogenated compounds such as bis(alkyl ether)tetrabromobisphenol A or decabromodiphenyl oxide (DECA) may be used as flame-retardants for polyolefin foams, eventually using antimony oxide, metal oxides, boric acid salts, and metal hydroxides as synergist.92 For example Weil and Levchik93 reported that using suitable amounts of DECA and Sb203, polyethylene foams rated UL94 HF-1 are obtained. 

The sulfur foams for these tests were foamed-in-place with pilot field equipment at a foaming rate of 100 lb/min. Installation, instrumentation, and performance of these tests have been reported in detail (1,2). Field surveillance data and sample analysis over two years so far indicate design insulation effectiveness and property integrity (Figures 1 and 2, Table I). 

The density and moldability of urethane foam is greatly influenced by the choice of the catalyst system and concentration, due to the effect of catalysts on the foaming rate (25)(26). 

Example 1 Hydrostatic Pressure Calculation. The following is an example of the foam density calculation. Because the calculation is an iterative process, the example will be in tabular form in order to account for each interval. The example has a few characteristics that should be noted. First, the pressure column is in absolute rather than gauge pressure therefore, standard atmospheric pressure must be added to the pressure. Also, foam rate and foam velocity have been calculated but are not necessary for this example. The surface conditions at which the foam was pumped were as follows ... 

Optimization of foam density uniformity, batch consistency, and thermal properties was performed and showed that a foaming rate of 3.5°C/min and a graphitization rate of l°C/min produced the best foam structures. 

Density Uniformity The first characterization of the foams was the measurement of the density uniformity after carbonization. Several billets of foams were made with two dificrent foaming rates 3.5°C/min and 10°C/min. Test billets were heat treated in the top and bottom positions in the furnace, as illustrated in Figure 3. This provides an understanding of the temperature uniformity within the furnace and its effects on the resulting foam. Table 1 reports the density uniformity for the billets processed at different foaming rates and positions in... 

Foaming Rate pc/min] Avg. Density Max Deviation Avg. Density Max Deviation... 

Fig, 6,3 Concentration relationships of the collapse rate of bubble foam (O) and high-expansion foam ( ) surface tension of the aqueous solution of C]o-Cn sodium alkyl sulphates ( ) and the relative residual concentration in die dispersion medium of a high-expansion foam in wt% ( ) foaming rate 0.83 cm /s (O), 13.5cmVs( ) ... 

Fig. 6.4 Effect of NaCl on the formation of high-expansion foams from 0.3% sodium alkyl sulphate solution of foaming rate Wo=12.8 cmVs, CNaci 0 ( ), 10 ( )> 30 (o), 50 (A), 120 ( ) g/l...

Reasons for use improve compatibility with other additives and polymers, improve flame resistance, improve low temperature performance, increase chain mobility, increase filler loading, increase flexibility and elongation, inflnence blood compatibility, lower glass transition temperature, lower viscosity, lower processing, gelation and fusion temperatures, modify foaming rate and microcellular stractirre... 

Foaming] rate of evaporation too fast/liquid downflow over foam too low. See general causes Usted in Section 1.12. 

One-part urethane adhesives have been used for many years as high performance sealants. In this capacity they provide a useful combination of strength, flexibility, and elastic recovery. As adhesives, these systems have limited use im-less formulated to overcome their inherent disadvantages. One-part polyurethane adhesives are typically moisture-cured and rely on a multistep reaction sequence as follows isocyanate reacts with water to form carbamic acid, the unstable car-bamic acid loses carbon dioxide and generates an amine, the amine reacts with additional isocyanate to form a urea, and the urea reacts with additional isocyanate to form a biuret, which includes a cross-link. Unless it diffuses out of the system, the CO2 can cause foaming. Formulators learn to minimize the isocyanate content (%NCO) of a system in order to balance cure speed with foam control. Cure speeds—and foaming rates—of these systems decrease from the outside in and vary with the amount of atmospheric moisture in the air, which changes hourly and seasonally. 

Covalent incorporation of anticancer compounds DB-67 and doxorubicin into polyurethane foam Rates were dependent on temperature and chemical structure of the drug Differential release of covalently bound drugs [30]... 

Figure 8 represents the attenuation of (a) 22D and (b) 42D coaxial cables. Newly developed coaxial cables show lower attenuation values for all frequencies. This was caused by the high foaming rate of newly developed cable. The detailed attenuation and propagation velocity were summarized in Table 2. About 6 8% of attenuation reductions were achieved in new coaxial cables. 

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